Question about "ceramic" abrasives

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Vicv

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Aug 22, 2011
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Ok. This use of the term ceramic has gotten me confused. You have man made oil stones. They're usually either made of AO or Sic which are both ceramics but they're not called ceramic stones. Then there's water stones that are also made of those compounds but not called ceramic. Then there's the ceramics water stones like Shaptons and sigmas and such that are also made of AO or Sic. Then you have plain abrasive belts which are AO or Sic or zirconia which is also a ceramic but not called ceramic. Then there's belts like norton blaze or 3m cubitron which are called ceramic belts but they're made of those compounds. So from what I can gather almost all man made abrasives are ceramic but they're not all referred to as ceramic. Why? It's very confusing
 
You are correct. In terms of scientific definitions, AO, ZrO, SiC, BC, CBN are all ceramics.

"Ceramic materials are inorganic, non-metallic materials made from compounds of a metal and a non metal."--wikipedia
http://en.wikipedia.org/wiki/Ceramic_materials

One should modify that definition to include metalloids as well as metals (for example, silicon and boron are "metalloids").
http://www.chemicalelements.com/groups/metalloids.html

In the forums, we often don't use scientific terminology. So here, informally, "ceramic" almost always only refers to a sharpening stone which is aluminum-oxide (AO). Not only that, "ceramic" usually means the very hard form of aluminum oxide, which is usually made with a very hard binder, or sintered together.

Informally, "ceramic" is considered to be different that, say, man-made waterstones that use aluminum-oxide. This is because waterstones are designed to break down quickly when sharpening, and have a softer weaker binder. Since man-made waterstones are designed to be similar to natural waterstones, they are put in a category which is separate, because waterstones are rather different than say, oil-stones and other abrasives.

So mostly, in informal discussions, you can replace "ceramic" with "aluminum oxide with a hard binder".

An exception is for flexible sanding paper and belts; then the binder for aluminum oxide "ceramic" need not be hard. The other ceramics (such as ZrO, SiC, etc.) are usually discussed by name. For example,"I used a ceramic belt (aluminum oxide), and then switched to SiC." Or,"After sharpening on a 2000 grit ceramic stone, I switched over to an 8000 grit (man made) waterstone."

Only sometimes in these forums, when there is are more technical use of the term "ceramic" will it actually mean, scientifically, all ceramics. btw, the above is not not some rule written in stone, but simply what I personally have observed.

Sincerely,
--Lagrangian
 
The term 'ceramic' refers to a process of manufacture, as opposed to the material itself. As I understand it, it basically implies the material was fired in a kiln to extremely high temps, to essentially 'fuse' the material together (as in 'fused alumina', which is what most so-called 'ceramic' hones are made of). I think the word itself is a derivation of a Greek word meaning 'pottery', which is made of different materials, but still fired in a kiln to extreme hardness.

The common characteristic I see, in true ceramic hones, is that they don't dish, break down or abrade away like other stones & abrasive products do. I'm sure that's a direct result of the manufacturing process itself, as opposed to whichever base material is integrated into it.

According to Wiki ( http://en.wikipedia.org/wiki/Ceramic ):
"A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling."
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Ok. Obsessed with edges. Your definition of ceramic for bench stone was fined with high heat and pressure basically. That's sintering I believe. Like sigma power II's. But regular sigmas are also ceramic but not sintered. And I use AO belts for my grinder to sharpen but they're no consider ceramic. Yet the blaze belts are also AO but called ceramic. So I guess with bench stones ceramic refers to a more resilient binder. It's just strange because say kings and naniwas are both water stones and they wear quite quickly. Nortons are also water stones but wear less quickly. But then the sigma power select II's are ceramic but wear very quickly. It just seems ceramic is a term thrown around by companies but doesn't really mean much except as a rule they wear less
 
Vicv said:
Ok. Obsessed with edges. Your definition of ceramic for bench stone was fined with high heat and pressure basically. That's sintering I believe. Like sigma power II's. But regular sigmas are also ceramic but not sintered. And I use AO belts for my grinder to sharpen but they're no consider ceramic. Yet the blaze belts are also AO but called ceramic. So I guess with bench stones ceramic refers to a more resilient binder. It's just strange because say kings and naniwas are both water stones and they wear quite quickly. Nortons are also water stones but wear less quickly. But then the sigma power select II's are ceramic but wear very quickly. It just seems ceramic is a term thrown around by companies but doesn't really mean much except as a rule they wear less
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It may also be the process of manufacturing the abrasive itself too (aside from the hone as a whole). Some versions of aluminum oxide are known to be 'friable' (particles break down to smaller size), and others not. The difference may be in the way the abrasive is manufactured, if it goes through a 'ceramic' process itself. I'm speculating, but that may account for some of the 'ceramic' labelling of other products, like waterstones & belts, assuming their abrasive particles remain a constant size, even as the hone itself abrades away and breaks down, or as particles come loose from the substrate/binder.
 
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Most AO abrasives keep a constant size as they abrade away. Sic fractures and gets finer in use which can be nice depending on application but a lot of AO abrasives keep a more or less constant grit size and they're not listed as a ceramic. I'm really not trying to be argumentative here as I'm not really like that and my experience is vastly lower than a lot of the people here. I've never even used a "ceramic" abrasive yet but none of the answers really are a concrete reason. Now I know you're speculating yourselves which is greatly appreciated. I guess it's just one of those things that doesn't have a concrete explanation. There are so many variables between abrasives even in one companies products let alone between companies. And I'm not singling out obsessed with edges. Lagrarian I also appreciate your help and you explanation also made sense. It just seems people seem to think the ceramics are the best in their given field and I was wondering why because even in the product description I can't really find any difference besides being called ceramic
 
I think the term "ceramic" exists in several different communities, and means slightly different things in each community:

(1) In the pottery and tile industry, ceramic means stuff which was fired/sintered in a high temperature kiln (defined in terms of manufacturing process).
(2) In materials science, ceramic means hard brittle inorganic material formed by chemically combining a metal/metalloid with a non-metal (defined only in terms of the material, not how it was manufactured).
(3) In knife sharpening, it means hard aluminum oxide.

So I think there is reasonable truth on all sides of the discussion.
It's just which definition or community you want to use. For example, if you go to a scientific conference on material science, you will see (2). But here, in a knife forum, you will see (3). And if you went to a pottery or tile factory, you would see (1).

Sincerely,
--Lagrangian
 
We're all still learning as we go. :)

I was searching the web for abrasives (generally) in the last few days, and saw that a lot of manufacturers of abrasive powders (AlOx, SiC, CBN, etc.) have seemingly vast arrays of variation in their products. Many more of which, I found, were listed as friable (talking about AlOx), some listed as not friable, and many others listed as 'somewhat' or 'semi' friable. This was an eye-opener for me, as I previously assumed most/all AlOx abrasives didn't break down. This is why I brought up the possibility of a 'ceramic' process making a difference in how/if they break down.
 
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(3) In knife sharpening, it means hard aluminum oxide.

Yes ceramic does mean different things in different industries. From your quote above Sigma stones are Silicon carbide and they're ceramic so I don't think your statement is always correct but yes usually a harder AO is deemed ceramic. It's the power equipment where things get farther away from the norm. 3M Trizacts are a very hard abrasive and they work a long time and they're AO but they're not ceramic. Same as Norton Norax belts. But now Norton has a ceramic Norax. That's what started me wondering about all this because their description of them seemed the same as the original except they last 30% longer. Well everyone says their new product lasts longer than all the rest. But besides from the new ceramic moniker they look and are designed basically the same. They may just use a new particle structure but now call it ceramic. I'm beginning to think it's a very general term to make their product look better. I have the lansky kit which comes with a 1000 grit ceramic hone. It's white and has a ceramic "look" to it but aside from being quite fine I can't see a difference. It does seem to have it's grit more bound up in the binder but that could just be because it's smoother. I'm not sure how abrasives are made exactly but it may just be that ceramics are abrasives which are finished with heat where say a King stone is just a slurry of binder and AlOx injected into a mould and pressurized so it stays together. That would actually make sense
 
Vicv said:
(3) In knife sharpening, it means hard aluminum oxide.

Yes ceramic does mean different things in different industries. From your quote above Sigma stones are Silicon carbide and they're ceramic so I don't think your statement is always correct but yes usually a harder AO is deemed ceramic. It's the power equipment where things get farther away from the norm. 3M Trizacts are a very hard abrasive and they work a long time and they're AO but they're not ceramic. Same as Norton Norax belts. But now Norton has a ceramic Norax. That's what started me wondering about all this because their description of them seemed the same as the original except they last 30% longer. Well everyone says their new product lasts longer than all the rest. But besides from the new ceramic moniker they look and are designed basically the same. They may just use a new particle structure but now call it ceramic. I'm beginning to think it's a very general term to make their product look better. I have the lansky kit which comes with a 1000 grit ceramic hone. It's white and has a ceramic "look" to it but aside from being quite fine I can't see a difference. It does seem to have it's grit more bound up in the binder but that could just be because it's smoother. I'm not sure how abrasives are made exactly but it may just be that ceramics are abrasives which are finished with heat where say a King stone is just a slurry of binder and AlOx injected into a mould and pressurized so it stays together. That would actually make sense
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That makes the most sense to me, too. There's also the question of how much heat is used. With all of the ceramic processes I've read of, they all involve extremely high temps (~1000 - 1500F or more), which is high enough to change the structure or physical properties of the AlOx. It may be that other hones are also produced in a heated process, but at much lower temps to cure the binders involved, without altering the physical properties of the abrasive itself.
 
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I think we might be on to something! Even if it's not correct it is to me so I can stop wondering about it. High heat makes ceramic which somehow makes it better
 
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